1. Field of the Invention
The present invention relates to a photographic printing shutter employed when an image recorded on an original-image recording film such as a negative film is printed onto a photosensitive material such as photographic paper.
2. Description of the Related Art
A shutter used in a photographic printer, for allowing printing light to pass between a negative film and photographic paper and cutting off the printing light therebetween, is generally constructed in the following manner. Shutter bodies supported by bearings are energized by an urging force produced by a tensile coil spring or the like so as to be brought into a state in which the shutter bodies cut off the printing light. When an image is to be printed, the shutter bodies are withdrawn from the axis of the printing light against the urging force due to the exciting force of a solenoid to thereby release a printing optical path (i.e., to allow the printing light to pass between the negative film and the photographic paper).
Therefore, shutter bodies each having a large area are required to allow the shutter bodies to reliably open and close a printing-light transmissive window. The more the area of the printing-light transmissive window increases, the more shutter bodies having larger areas are required.
Shifting each of the shutter bodies to a releasing position by the solenoid and moving each of them to a closing position by an urging force of the coil spring leads to the problem that the traveling speed of each shutter body is not kept constant and releasing times differ from each other at individual points in the printing-light transmissive window, so that an exposure time at the entire area of a printing image becomes nonuniform (i.e., the shutter causes nonuniformity).
When an image recorded on a negative film is printed onto photographic paper by the photographic printer, a process for determining a standard exposure condition is required prior to a printing process.
To this end, an ND filter corresponding to a light attenuating filter is inserted into an optical path for printing and exposure so as to expose the photographic paper to light under an exposure determined based on a measured value of the intensity of light and a standard exposure condition. The ND filter is normally disposed on the optical path and adjacent to a printing light source to facilitate the removal of the ND filter.
Since, however, the ND filter is disposed near the light source, characteristics of the ND filter vary due to the heat produced from the light source. Thus, the ND filter may be mounted to a portion away from the light source. However, since it is necessary to remove the ND filter upon printing, the ND filter needs to be disposed in a position where an operator can easily work. Therefore, the ND filter is complicated in structure.